Corbyn appeared to mutter the words after he sat down following an exchange with May at the weekly Prime Minister’s Questions session during which she mocked him for not calling a vote of confidence in the government.

“I know it’s the Christmas season and the pantomime season,” May said. “He’s going to put a confidence vote, oh yes he is, oh no he isn’t. I’ve got some advice. Look behind you! They are not impressed and neither is the country.”

A number of Conservative MPs asked Speaker of the House John Bercow to intervene but he refused, saying he hadn’t heard Corbyn utter the phrase.

That resulted in Tory MP and Leader of the House Andrea Leadsom critcizing Bercow, saying the speaker had not apologized for calling her a “stupid woman” earlier in the year.

May then said: “I think that everybody in this house, particularly in this 100th year of women getting the vote, should be aiming to encourage women to come into this chamber, and to stand in this chamber and should therefore use appropriate language in this chamber when they are referring to female members.”

According to the Guardian, Corbyn’s spokesman said “he did not call her a stupid woman” but said “stupid people.”